In a
medium bowl, mix together the icing sugar and flour. Mix in butter with a fork
until it is in small crumbs. Stir in the egg and vanilla until the mixture
forms a dough. The texture should be slightly moist. Add more butter if it is
too dry, or more flour, if the pastry seems greasy. Shape pastry into 3cm
balls, and press the balls into tart moulds so that it covers the bottom, and
goes up higher than the sides. Use 2 fingers to shape the edge into an A shape.

Preheat
the oven to 230 C / Gas 8. Combine the caster sugar and water in a medium
saucepan, and bring to the boil. Cook until the sugar is dissolved, remove from
heat and cool to room temperature. Strain the eggs through a sieve, and whisk
into the sugar mixture. Stir in the evaporated milk and vanilla. Strain the filling
through a sieve, and fill the tart shells.

Bake for
15 to 20 minutes in the preheated oven, until golden brown, and the filling is
puffed up a little bit.